There are many situations in which it is desired that a prototype or low-volume production tool be made from a master model constructed from relatively low heat-resistant material; that is, the material out of which the model is constructed either softens and/or melts at a relatively low temperature, or is combustible at comparatively low temperatures. Examples of such materials of construction for master models that would be desirably accommodated include wax, wood, plastic and similar materials.
It is known to use zinc alone in spray forming processes on such low heat-resistant materials, but the resulting tool is relatively soft because of its exclusive, or near-exclusive zinc content. As a result, tools of only very limited application may be formed in such a manner. These tools are normally limited to prototype applications because they do not possess sufficient durability to withstand even low-volume production manufacturing.
Conventional thermal spray form molding has utilized metals which require substantial energy input, which is typically manifest as heat energy, to moltenize and make the metal sprayable. Because of the high temperature of such a moltenized metal when it strikes the master model, the model has typically been required to be constructed from high heat tolerant material, such as ceramic, in order to survive the spraying of such molten metal thereupon. Because the original model is not typically cast directly in ceramic, multiple steps are required to finally establish a ceramic master model from one that has been constructed, for instance, by rapid prototyping methods such as stereo lithography, or which are constructed out of other types of low-heat resistant materials such as wood, wax and plastic laminate.
Because of the expense and delay associated with the usual multi-step process required to establish the ceramic master model, it is highly desirable to be able to perform spray form techniques directly upon the surface of an original model constructed from such rapid prototyping methods and low-heat resistant materials.
In at least one embodiment, the present invention takes the form of a method for spray forming an article, such as a low-volume stamping tool. The method includes spraying a plurality of metal streams upon a low-heat resistant model and thereby forming a spray formed article. Each of the plurality of metal streams is composed of moltenized droplets, and as between the plurality of metal streams, each is composed of different constituent elements. According to the invention, conditions of the metal streams are controlled, particularly around the time that the droplets first land, to assure that excessive heat energy contained therein is for all practical purposes, dissipated essentially immediately upon contact. In this way, if there is heat imposed on the model from the sprayed metal, it is sufficiently transitory that even low-heat resistant materials remain unaffected. The spray conditions are controlled in such a manner that the individual metal droplets forming the metal streams remain substantially segregate; that is to say, touching one another, but without intermixing across droplet surface boundaries. The droplets are held together based on mechanical adhesion that occurs when the semi-molten droplets come into contact with one another.
The segregated state is maintained through out solidification so that the resulting spray formed article is composed at least partially of psuedo-alloy; that is, commingled droplets of different elemental metals, but without intermixing into true alloys. The article may also be considered a psuedo-alloy based on a more global perspective; that is, the individual droplets may not be highly commingled, but different elemental deposits that are established in the spraying process are intermingled.
In another aspect, the invention includes the control of the relative proportions utilized of each of the metal streams that are differently composed on an elemental basis in a manner that institutes prescribed performance characteristics in the resulting spray formed article. In this way the qualities of the finished spray formed product can be manipulated to assure that the article is suitable for its intended use; as an example, as a spray formed stamping tool manufactured for use in low-volume production processes.